Oscillation generator



- April 29, 1930. s, OHL 1,756,130

050 ILLATION GENERATOR Filed Aug. 14, 1925 INVENTOR ATI'ORNEY PatentedApr. 29, 1930 uNiTEo I STATES PATENT OFFICE memes; o'HLjor jnEw YoEx, N.Y., ASSIGNOR "110 AMERICAN TELEPHONE AND TELEGRAPH COMPANY, A.CORPORATION or NEW YORK OSCILLATION' GENERATOR This linventionrelates tooscillation generconstant thefrequency of oscillations.

It: has: been known that'piezo-electric devices' nay be employed tocontrol the frequencyof oscillations generated by space discharge tubeoscillators. The piezoelectric device's so'u'sedfor controlling thefrequency ofthe oscillators were crystals cut from quartz; and it wasfound that such crystals responded to anumber of frequencies Withvarying degrees ofactivity. There is usually one natural frequencyatwhich the crystal gives its greatest response. Generally, however;oscillators which'have piezo-electric devices associated therewith forcontrolling the frequency ofthe oscillations are usually operated at thefrequency at which the piezoelectric device gives its greatest response.

Inthe past" it'has. been customary to cut these piezo electric crystalsused inoscillation generators-from quartz so that the dimension inthe'fdirection ofthe axis of vibration of the'crystal is small as comparedto the other dimensions. It ha'sbeen found that crystals so out have anumber of "frequencies, which arenot'i'in the same neighborhood, towhich they respond in a very large degree. Maximunr eificieiicy has been'obtained when the oscillation generator was operated at a frequencywhich corresponded to the natural frequency of the crystal-forthegreatest response piezG-electric controlled oscillationgenerato-rs'has been thefailure of the piez'o-electric crystal tostart-in operation without the aid of an initial mechanical jar. Anotherdifliculty has been the failure to maintain the crystal inoperationafterbeing started. Because of these. difficulties the'application ofpiezo-electrio devices hasbeen-limited.

.Itis' an object of the present invention to control within'narr'owlimits the frequency of oscillations generated by an oscillatorcontrolle'd b-y aupiezo-electric device. Another object of thisinvention is to provide means for starting the pie zo-electric device invibration .withoutithe aid of any external mechan- Or ie of thechiefdifiiculties in the use of- Application filed August 14, 1925. SerialNo. 50,336.

ical forces. Another object ofthe invention is to provide means forkeeping the piezoelectric devices in vibration after being started, andit. is a further object to employ the capacity between the electrodes ofa space discharge tube for coupling the input and output circuits of thetube in which such a piezo-electric device is present.

Acircuit arrangement for producing these results is shown in theaccompanying drawing, which comprises a circuit electrically tuned togive oscillations of the desired frequency. 1 is a space discharge tubeworking onthe thermionic principle, including a cathodc2; an anode 3,and an input or grid electrode 4. The grid 4 is connected to oneterminal of the piezo-electric device 5, while the other terminal of thepiezoelectric device is connected to one terminal of an inductance 6.The cathode 2 is heated to incandescence by means of a battery 7. Asource of potential 8 supplies space current to the anode 3 through theinductance 9. A condenser 10 is connected across the terminals of thesource of-potential 8 in order to form a path of low impedance foralternating currents. A resistance 11 is connected between the gridelectrode 4 and the cathode 2 in order to maintain the grid electrode ata suitable negative potential with respect to the cathode. A condenser12, shown in dotted lines, represents the inherent capacity between thegrid electrode 4 and the anode 8, including the capacity of the leadsconnected thereto. It is this capacity between the grid electrode 4 andthe anode 3 which produces a reaction of the'plate circuit on the gridcircuit in order to produce sustained oscillations.

The piezo-electric device 5 comprises conductive plates 13 adjacent tothe opposite sides of thecrystal. Thecrystal is prefer- I ablydisk-shaped, cut from quartz along one jected toan' electrostatic fielda physical deformation occurs along the axis of the crystal. The signsof the charges produced in the first case depend upon the character ofthe stress, that is, whether tension or compression, Whereas in thesecond case the physical deformation due to the action of theelectrostaticc field depends upon the direction of the field.

If'the stress changes from com;

pression to tension, or vice versa, the signs of the'electric'chargesfonthe faces of the crystal are reversed, whereas 1f theelectrostatic field is alternately reversed tliecrystal undergoesalternately contraction and elongation in the direction of the axis. Inother words,the crystal vibrates in an electrostatic the chargeisalternately re-.

in the provision of means for starting the piezoelectric device invibrationv atone of its natural frequencies without the aidfof anymechanical ar or other external force.

This means comprises an inductance for feeding some of-the energy in theplate circuit back to the grid circuit, and therefore pro;

vidcs for the production of a varying potential on the. terminals ofthepiezoelectric I has a maximum impedance is'slightly less device. Thusthe potential on the terminals of the pieZo-electric device is graduallybuilt up to assist in starting it in vibration. This advantageconstitutes a. material improvement over any of the crystal-controlledoscillators known heretofore.

Another advantage of the present invention lies in the provision ofmeans for insuring the continuity of the vibration after started. Thismeans comprises, the connection of a source of electromotive force,which may be the source employed for. supplying V herein means any bodyor substance capable the plate circuit with the necessary: space:cur-

rent, across the terminals ofthe piezo-electric This insures thecontinulty of the device.

' action of the piezof-electric device after it is source of potential 8and inductance 9 may,

if; desired, be considered the output circuit,

and the circuit including grid electrode 4,

cathode 2, source o'fpotential 8, inductance 6 w and the.picnic-electric device 5 may be con;

sidered the input circuit. The input circuituand the output circuit arecoupled through "the electrostatic capacity between the grid electrodevand the anode of the space discharge tube 1. The condenser 10 shunts thesource of electromotivc force 8 for alternat- .in currents. Part oftheenergy in the out-i insurev its starting whenever ...Furthermore, thesource 0f.potent1ali 8 is connected across the terminals of thepiezofound lthat: a piezo-electric I his also constitutes a ma putcircuit is fed back to the input circuit through the mutual inductancebetween windings 6 and 9. This energy so fed back tends to produce avariation in the potential across the piezo-electric device in order torequired.

electric device 5, through the resistance 11 and tends to maintain'thecontinuity ofthe vibrations of the piezo-electric device after it isstarted. "The resistance 11' is used here instead of a battery tomaintain the grid electrode at an appropriate negative potential withrespect to the cathode. This means ofmaintaining the grid negativeoperates only when there is a convection current between the cathode andthe grid electrode, that is, it tends, to main: tain the grid electrodenegativewith respect to the cathode during that part of the cycle inwhich the grid electrode hasa positive charge impressed thereon. Whenthe grid electrode becomes positive itattracts elec,-.

tronsiandthe currentflows through the resistance 11 During the! rest ofthe, cycle there is no fiow ofelectrons from the cathode to the gridelectrode; A rectified current is therefore established through theresistance '11 and this therefore lowers the potential of the gridelectrode with respect to the cathode. a

The frequency at which the output circuit than the natural frequency atwhich the piezo-electric device is vibrated. In one capable of producinga more stable oscillatory condition, The. piezo-electric device wasstarted automatically invibration whenever required, and was maintainedin vibrationcontinuously until the source of potential was disconnected.I M r The term. piezo-electric device as used of generating anelectromotive force in response to a change'ln-pressure. I VVhlle thislnvention has been disclosed in one embodiment which is deemed.desirable,

ity is capable of embodiment in other and widely variedorganizationswithout departmg from the spirit and scope of the appended claims.

That is claimed is:

1, In an oscillator,a'three-electrode space discharge device, aninputcircuit connected to NHL arrangement actually operated under theseCO11(il1l31011S,'1t was found that thesystem was two electrodes of saiddevice, an output circuit connected to one of said electrodes and athird electrodemea'ns whereby said input and output circuits maybecapacitatively coupled to.

produce sustained oscillations, an inductance having a low distributedcapacity,.a source of I potentia-L'ancl a piezo-electric' device as anelement of said input circuit to govern the fre lations, apiezo-electric element associated with the input circuit having anatural frequency substantially the same as the frequency for which theoutput circuit has a high and predetermined impedance, and means forstarting said piezo-electric ele ments in vibration and for maintainingthe continuity of said vibrations after being started.

3. In an oscillation generator, a threeelectrode space discharge devicehaving input and output circuits, said circuits being coupled by thenatural capacity of their conductors in order that oscillations may besustained, means for controlling the generation of said oscillations,said means comprising a piezo-electric oscillator arranged in said inputcircuit, said piezo-electric oscillator having substantial inductivereactance at some frequencies and substantially no reactance at otherfrequencies, and an inductive coupling between said input and outputcircuits for I supplying energy to said piezo-electric oscillator tostart and continue said piezo-electric oscillator in vibration at thefrequency at which it exhibits asubstantial inductive reactance.

4. Means for generating oscillations, comprising an electrical dischargetube having a cathode, an anode and an impedance-varying element, aninductance, a piezo-electric device, and a source of potential, part ofsaid inductance being included in an output circuit along with saidsource of potential, said anode and said cathode, the rest of saidinductance being included in an input circuit along with saidpiezo-electric device, said impedancevarying element and said cathode,said input and output circuits being coupled by the inherent capacitybetween said anode and said impedance-varying element, said inductancebeing arranged to feed energy from said output circuit back to saidinput circuit in order to insure the starting of said piezo-electricdevice, said piezo-electric device being also connected across saidsource of potential to render the action of said piezo-electric devicecontinuous after being started.

5. Means for generating oscillations, comprising a space discharge tubehaving an anode, a cathode and a grid, an inductance, input and outputcircuits for said tube, each circuit including a part of saidinductance, a

piezo-electric device and a source of potential, said inductance socoupling the input and output circuits as to set up a potentialsufficient to start said piezo-electric device in vibration.

said source of potential being connected across the terminals of saidpiezo-electric device to render the vibration of said piezo-electricdevice continuous.

In testimony whereof, I have signed my name to this specification this13th day of August, 1925.

RUSSELL S. OHL.

